Why is moment ##F.S## instead of ##F.\frac{S}{2}## for this diagram?

[Benjamin_harsh]

Homework Statement

Why is moment $F.S$ instead of $F.\frac{S}{2}$ for this diagram?

Relevant Equations

$F.\frac{S}{2}$

Why is moment $F.S$ instead of $F.\frac{S}{2}$?

 

[Orodruin]

Why do you think it should be FS/2?

 

[Benjamin_harsh]

Why do you think it should be FS/2?

Because pivot is at $\frac{S}{2}$.

 

[Orodruin]

Because pivot is at $\frac{S}{2}$.

And the forces?

 

[Haorong Wu]

Because pivot is at $\frac{S}{2}$.

But there are two $F$.

 

[Benjamin_harsh]

But there are two $F$.

So, How does it answer my question?

 

[Haorong Wu]

So, How does it answer my question?

$2*F \cdot \frac s 2 = F \cdot s$. The direction of the two moments are the same, so they add up.

 

[collinsmark]

@Haorong Wu

Please do not provide the OP's entire solution directly, for posts in the Homework Help subforum. It is against the forum rules.

See Part 8 of the "Guidelines for Students and Helpers," Helpers: don't provide the entire solution.
https://www.physicsforums.com/threads/guidelines-for-students-and-helpers.686781/

 

[Benjamin_harsh]

$2*F \cdot \frac s 2 = F \cdot s$. The direction of the two moments are the same, so they add up.

Thank you

 

[Haorong Wu]

@Haorong Wu

Please do not provide the OP's entire solution directly, for posts in the Homework Help subforum. It is against the forum rules.

See Part 8 of the "Guidelines for Students and Helpers," Helpers: don't provide the entire solution.
https://www.physicsforums.com/threads/guidelines-for-students-and-helpers.686781/

Oh, I'm sorry. I didn't read that.

 

[Benjamin_harsh]

There is another way. Since Pivot is not at center. $\sum M = F.(S-X) + F.X$

so $\sum M = F.S$ since it is clockwise direction, there is no need to multiply -ve sign to it.

 

[haruspex]

since it is clockwise direction, there is no need to multiply -ve sign

I thought you were using the usual convention that anticlockwise is positive.